1. Field of the Invention
The present invention relates to a projection type display apparatus using a lamp such as a xenon lamp for a light source and to an apparatus for cooling that lamp.
2. Description of the Related Art
An LCD projector is widely used as a video display apparatus for a large-sized screen. An LCD projector, as is well known, is constituted such that radiated light from a light source is condensed and irradiated onto a liquid crystal panel and the light modulated by the liquid crystal panel corresponding to a video signal is projected onto a screen.
A discharge lamp is widely used as a light source of the LCD projector. Among these discharge lamps, a xenon lamp has a strong spectrum component of a red color as compared with other discharge lamps (ultra high voltage mercury lamp, etc.) so that it has an advantage that natural color rendering properties can be realized without emphasizing a blue color or a green color too much.
However, on the other hand, the heat-radiation value becomes great, because the xenon lamp has a need for high wattage for realizing the same brightness as that of other discharge lamps. Therefore, it becomes very important for an LCD projector using a xenon lamp as a light source to cool the xenon lamp.
Heretofore, it is known that for an LCD projector using a xenon lamp operating as a light source, a fan is disposed on the rear side of the xenon lamp and air suction is carried out by the fan such that cooling air is taken in from the front side of the xenon lamp (for example, see Patent Reference 1).
FIG. 1 is a diagram showing a brief overview according to such a conventional cooling system. A heat sink 52 is mounted on a xenon lamp 51 and the xenon lamp 51 and the heat sink 52 are contained in a lamp duct 53.
A fan 54 is disposed on the rear side (right direction in the drawing) of the lamp duct 53. Air suction is carried out by the fan 54 such that cooling air is taken in from the front side (left direction in the drawing) of the lamp duct 53 into the lamp duct 53. This air is exhausted to the rear side through the fan 54 after passing through the xenon lamp 51 and the heat sink 52.
[Cited Patent Reference 1] Jap. Registered Pat. No. 3348653 (see paragraph Nos. 0004 and 0017, FIGS. 1 and 6)
However, there are disadvantages such as (a) or (b) as described below in the conventional cooling system.
(a) It is important to prevent the temperature increase of a glass (usually sapphire glass is used) which is disposed at the front face of the xenon lamp and operates as a light radiation plane in order to maintain the temperature of the xenon lamp. However, in a case when air suction is carried out by the fan on the rear side of the xenon lamp, it is not easy for the air to hit the glass directly and even if it hits, the force thereof is weak, so that it is difficult to adequately prevent the temperature increase of the glass.
In addition, if it is conversely attempted to prevent the temperature increase of the glass, the rotational speed of the fan should be made considerably high or a considerably large-scaled fan should be used. However, this will create an increase in ambient noises and the whole LCD projector becomes large sized.
(b) The temperature of the fan will increase, because high temperature air warmed by the xenon lamp and the heat sink will hit the fan. As a result, lubrication oil applied to the rotational axis of the fan motor will evaporate so as to increase rotational resistance thereof and at the same time abnormal noises will be generated or burning will occur in the fan such that the life time and the reliability of the fan will be lowered.